Multi-energy γ densitometry: analysis of composite materials

The application of multi-energy γ-ray densitometry to the composition analysis of bulk material steams is developed in both theory and experiment. In this technique, the differential attenuation of several energies of γ radiation through some material is used to determine the weight fraction of groups of elements (grouped by neighboring atomic number Z) in the material. The theory is analyzed in detail for the two-energy case and is then generalized to the N-energy case. The contributions of errors due to counting statistics, composition variations, heterogeneity, and in-scattering of the γ rays by the material are calculated. Computation of the in-scattering contribution was done using a computer code which uses multiple integration to calculate the number of singly scattered γ rays detected. Based on the laboratory work, a rugged version of the system was built and installed in a coal mine. This field instrument was compared with hourly chemical analysis of samples taken from the coal stream; the observed standard deviation between the two ash estimates was approximately 1% (absolute) for coal of nominally 10% ash, measured over several months of operation